well as my name may tell you i own a 1969 z28 rs. that's in fact matching numbers. now when you ask how do you know what it is do you mean if it's matching numbers or the right engine or what? if it's a NORWOOD car which on your Cowl would be NOR. if so UNLESS it'a an early 69 it should either have an X33 or X77 code on it. this will tell you it's a z. if it's an SS then you can have many other cowl tag numbers. now is it an RS? if so there's no really good way to prove it unless you have the original window sticker(like i do). if you would please email me some info. on your car and i will try to help you if you still need it. [email protected] i have multiple camaro books and a good bit of general knowledge so i should be able to help you out. now if yours is a VAN NUYS car on the tag it will read LOS12347*****, but these cars are much much harder to decode. that's what i own. it is actually REGISTERED by Jerry MacNeish (a very renouned camaro guy), except he had to go through the whole car because my particular van nuys car was missing the partial engine VIN. so he had to match the charaters on the black to the rest of the car, so as you can see van nuys cars are a bit more dificult. please go to see my car if you would like.... http://www.69zee.homestead.com/enter.html this will take you to the site so that you can see it if you would like to. but PLEASE PLEASE email me i can help with some info.